The synovial cyst of the spine may be caused by degenerative changes or instability of the spine [1–3]. The most common site of spinal synovial cysts is the lumbar spine [4]. Large synovial cysts can compress the nerve root and thecal sac, and then this compression can cause radiating pain in the lower extremities and back pain [2]. Unless conservative management such as aspiration and corticosteroid injection were effective, surgical resection of synovial cysts should be considered [5]. Microscopic cystic removal has become a widely used surgical method so far [6]. Recently, biportal endoscopic spine surgery has been gradually used for discectomy, decompression, and fusion surgery [7]. We have also removed the spine synovial cyst using biportal endoscopic surgery, which we would like to report together with a literature review.

A 74-year-old male patient suffered from low back pain with right radiating pain from 1 month ago. He squatted down and worked in the fields before developing the symptoms. At first, other hospital gave him medication suitable for the symptoms, but the pain did not decrease and rather weakness in the right lower extremity occurred.

On the physical examination, the power of ankle dorsiflexion on the right side was grade III and steppage gait was observed while walking. In simple dynamic radiographs, degenerative spondylolisthesis of grade I was found (Fig. 1). In magnetic resonance images, it was confirmed that a synovial cyst was present on the right side of L4–5 with facet effusion (Fig. 2).

The authors performed an ipsilateral biportal endoscopic surgery. The patient was placed in a prone position with general anesthesia. Two transverse skin incisions were made 2 cm apart at the margin of the interlaminar space under the C-arm guide. Subcutaneous fascia and muscles were split using a dilator, and then a 0° arthroscope was inserted. About 1 mm of partial laminectomy was performed at the right L4 distal part and L5 proximal part, and then partial flavectomy was performed. The synovial cyst was found and we easily resected the cyst without facet injury (Fig. 3). The pathology of the cyst was confirmed as a synovial cyst.

In postoperative magnetic resonance imaging, the synovial cyst pressing on the dura was no longer identified (Fig. 4), the symptoms improved, and the foot drop returned to normal a week after surgery. There was no pain or recurrence of the cyst after 1 year of surgery.

The patient provided written informed consent for the publication of clinical details and images.

Spinal synovial cysts caused by degenerative changes or instability occur in old people, especially older than 70 years old [8]. Among the synovial cysts in the spine, about 10% cause symptoms such as low back pain or radiating pain. Almost synovial cysts are located in the lumbar spine [4]. Since the L4–5 level is the most flexible segment in the spine, degenerative spondylolisthesis is easily generated in the area, and synovial cysts could be easily generated accordingly [9].

If symptoms appear due to a synovial cyst in the spine, conservative management should be attempted first. Conservative treatment includes cyst aspiration, which has a very high failure rate [9]. Microscopic surgery is a recent treatment of choice for symptomatic spinal synovial cysts [6]. But the ipsilateral microscopic approach involves partial laminotomy with medial facetectomy, it may induce postoperative segmental instability [10]. Recently, biportal endoscopic technique in the spine is a minimally invasive surgical modality and has been used gradually and widely [7]. As a biportal endoscopic spine surgery provides real-time magnification images of the surgical field through the endoscope, small surgical dissection can provide a sufficient surgical field to perform thorough and fine lumbar surgery [11].

In this case, complete removal of juxtafacet cyst was performed via an ipsilateral interlaminar approach and iatrogenic facet violation was avoided. As a result, postoperative instability in the facet joins has not occurred, and the degenerative spondylolisthesis did not worsen, resulting in no further radiating pain and recurrent synovial cysts. This is reported along with a review of the literature review.